Extreme ultraviolet (EUV) lithography technology is a pattern forming technology using a 13.5 nm wavelength light source, which is very short compared to the conventional photolithography technology using 193 nm light from an ArF light source.
This is considered a core technology for fabricating semiconductor devices having a line width of pattern with 22 nm or less.
The EUV light source is strongly absorbed by all materials naturally in existence, and, therefore, design of necessary equipment for processing in terms of form, structure etc. changes from the conventional photolithography.
Because EUV is so highly absorbed, for photolithography equipment, transmission optics are not used, and all optics in EUV optics are of the reflective type.
An EUV pellicle for lithography is for protecting a mask, is mounted on a mask, and is fabricated as a transmissive thin film.
While a pellicle made of a single thin film layer of silicon, that is, a pellicle for EUV lithography for which research has advanced the most may achieve adequate EUV transmission because a thin film is formed of mechanically weak silicon that is 100 nm or less, due to the low strength, fragility is a problem in which the pellicle is easily torn due to even a small impact, etc.
Accordingly, while a pellicle with an attached support structure in a honeycomb structure, etc. are being researched to improve the strength of a single silicon thin film, in this case, while it is possible to partially improve the problems of sagging, tearing, etc., a new problem occurs in which there is a non-uniformity of intensity of EUV light, etc. due to the shape and thickness of the support structure.
Further, there has been a problem in which it is extremely difficult to make an adequately microscopic support structure that can solve the problem of intensity EUV light becoming non-uniform.
Accordingly, there is a need for research on a pellicle for EUV lithography without a separate support structure and with improved strength and EUV transmission.
On the other hand, when unwanted particles become attached on a lithography mask surface during an EUV exposure, defects due to the particles are formed during pattern formation using lithography.
To prevent the particles from being attached on the surface, a pellicle is fabricated in a form that protects a mask pattern. However, because wavelength of EUV light is well absorbed by all materials, the pellicle absorbs the light, round-trip optical paths are formed because the protected mask is in a reflective form, and thus absorption occurs twice per pellicle layer. Accordingly, such a pellicle causes loss of light.
This can greatly reduce throughput of a semiconductor EUV lithography exposure tool.
Accordingly, a pellicle for EUV lithography is formed as a transmissive thin film and mounted on a mask to protect the mask.
A pellicle for EUV lithography for which research has advanced the most is one made of a single thin film layer of silicon. Because such a pellicle made of a single thin film layer of silicon is just a single thin film layer of mechanically weak silicon that is 100 nm or less, adequate transmission of EUV is achieved, however fragility is a problem due to the low strength, where the pellicle is easily torn due to even a small impact, etc.
Accordingly, while a pellicle with an attached support structure in a honeycomb structure, etc. is being researched to improve the strength of a single silicon thin film, in this case, while it is possible to partially improve problems of sagging, tearing, etc., a new problem occurs in which there is a non-uniformity of intensity of EUV light, etc. due to the shape and thickness of the support structure.
Further, there has been a problem in which it is extremely difficult to make an adequately microscopic support structure that can solve the problem of intensity of EUV light becoming non-uniform.
Accordingly, there is a need for research on a pellicle for EUV lithography capable of fulfilling requirements of both EUV transmission and strength.